1. Field of the Invention
The present invention relates to an improved apparatus and associated methods of measuring the length of an opening in a bone, so that an appropriate fastener for use in medically restoring the bone may be selected.
2. Description of the Prior Art
It has been known in both human and veterinary uses to employ a depth gauge to measure the depth of a hole in a bone. A fastener, such as a pin or a screw, for example, of appropriate length can be employed in a surgical procedure in facilitating repair or reconstruction of bones, which have suffered traumatic injuries or are damaged as the result of congenital deformities or are the result of disease or otherwise make it desirable to assist a bone during healing.
A variety of such surgical procedures are performed on human bones by orthopaedic, plastic, ear nose and throat, maxillofacial, neuro-, and general surgeons. These include a variety of emergency and elective procedures. Similar procedures are employed by veterinarians in their work.
Whether fixing a fractured bone, correcting a congenital or acquired bone deformity, or merely removing a portion of bone to allow access to deeper tissues and structures, many of the surgical procedures involve placement of screws or pins or nuts and bolts into a bone with or without plates or rods for added support. These screws are usually metallic, but in some cases, they may be made from other materials, such as polymeric materials capable of being ultimately broken down and absorbed by the body. Such screws are placed for fixation or securing of pieces of bone directly, or to secure other hardware, such as metal plates or rods, to the bones involved as part of a more complex construct designed to hold two or more pieces of bone together.
Several techniques are commonly employed. One or more of these may be done any one particular surgery. Isolated screws may be placed directly into one fragment of bone or placed across or through two or more bone fragments to hold them directly together. One or more screws may be placed first through a portion of bone and then through other hardware, such as metal plates or rods, which have openings or holes, to accommodate passage of the screw so that the resulting construct holds two or more pieces of bone together as one. Screws may be placed first through hardware such as a plate lying on the outer surfaces of two or more pieces of bone and then into the bone, to secure the plate to the bone fragments effecting a construct to “bridge” and secure together the bone fragments. This may apply to two or more pieces of bone which have been separated by traumatic fracture, or bones which have been cut apart and re-aligned by the surgeon to correct a deformity (a so-called corrective osteotomy).
Usually a precise length of a screw must be known to assure good purchase of the screw over its length and to assure that the screw is not so prominent as to cause a problem with other tissues on which it might impinge. Therefore, techniques for precise measurement of appropriate screw length must be employed. There are a number of recognized surgical complications which have occurred from screws which are too short leading to insufficient fixation and “pulling out” of the fixation hardware and loss of position of repaired bones. In other cases, screws which are too long have resulted in damage to normal structures, such as tendons, which have ruptured as a result of wear against screw ends protruding through bones.
In a general way, many bones can be viewed as a cylindrical structure with a thicker, stronger outer wall of the cylinder (known as the cortex) and a softer middle or inside portion (known as the medullary cavity). Bone can almost be viewed as a thick-walled hollow cylinder, though the softer middle does have some substance. Screws are usually placed in one of two fashions, so-called 1) “unicortical” and 2) “bicortical.” In unicortical placement, the screw extends through the outer cortex of one side of the bone and protrudes into the inner cavity. In bicortical placement, the screw is placed across the entire width of the bone, so that the screw enters through the outer surface or cortex of one side of the bone, extends through the inner cavity and then extends to, or just through, the outer edge or cortex of the bone across from the entry site. In general, bicortical placement results in a stronger purchase of the screw in the bone, but situations exist where only unicortical placement is possible or, in some cases, desirable. The screws are usually placed by preparing or drilling a pilot hole across the bone at the desired location for the screw. In bicortical placement, this pilot hole is drilled through the near or entry site cortex, through the medullary cavity and out through the exit site cortex (opposite the entry hole). In unicortical placement, this pilot hole is drilled through the near or entry site cortex and into or through the medullary cavity, but not through the cortex opposite the entry site (the so-called distal cortex). Even with unicortical placement, sometimes the depth of the “partial” bone hole is measured in order that the screw placed does not “bottom out” and the head protrude too far above the entrance hole.
In the process of fixation of two or more bone fragments, such as occurs with a fracture or break of a bone, the fragments are usually assembled or repositioned by manipulation, manually or with instruments, to reconstitute the normal shape of the bone. This is called “reduction of the bone or fracture.” The fragments are then held together manually by the surgeon and/or his or her assistants or held by clamps designed for that purpose. Screws may then be placed across the construct usually extending from the cortical surface of one bone fragment, across the plane of the fractured surface(s) and then extending to and through the outer cortical surface of the second bone fragment thus securing the two fragments together. In this case, the pilot hole will traverse the cortex of the first bone piece, cross the plane of the fracture, and then traverse the cortex of the second bone piece. Alternatively, or in conjunction with direct screw placement, after appropriate reduction of the bone, a metal plate designed for this purpose is placed on the outer cortical surface of the bone, so that a portion of the plate overlies or is in contact with each of the bone fragments. Screws are then placed through holes spaced along the plate for that purpose, into each segment of the plate adjacent to a bone fragment, into and across the adjacent bone fragment. The holes within the plate are usually contoured or countersunk within the plate to allow the head of a screw to sit within the depression of the countersink and exert pressure against the plate to secure it. These countersunk holes also decrease the prominence of the screw head above the plate. This construct allows the plate to “bridge” across and support the various bone fragments to hold them in proximity, so they are able to heal by the normal biological processes. The metal fixation devices maintain the bones in proper alignment for the normal or desired ultimate shape of the healed bone while the healing process takes place. In some situations, a rod may be placed through the inner cavity portion of the bone once all of the fragments have been reduced or aligned. One or several screws may be placed through the outer surface of the bone, through holes in the rod for that purpose, placed at appropriate positions along the length of the rod, and then out through the rod and through the cortical bone on the other side of the rod. This links together the rod and the various bone fragments, again for the purpose of maintaining alignment and allowing appropriate healing of the bone.
The screws, plates, and rods used in such a manner are typically made of metal of various types, but other materials have also been used, including some types which are ultimately absorbed by the body once the healing process has occurred. It is important to place screws of appropriate length to properly engage the bone and adjunctive fixation devices, but not so long as to impinge unnecessarily on other tissues.
In most cases, placement of screws involves drilling a pilot hole into or through the bone(s) and measuring the depth of the hole or the distance from the outer edge of the bone at the entry site of the hole to the outer edge of the bone at the exit site of the hole. The proper length of screw can then be inserted into the hole. The lengths and depths of such bone holes are measured by devices, which are commonly known in surgical parlance as “depth gauges.” In cases where a plate is used for fixation, typically, the plate is set on the surface of the involved bone, and the pilot hole is made by passing the drill bit through an existing screw hole in the plate down to the surface of the outer cortex of the bone, and then drilling through the adjacent bone. The plate is maintained in position overlying the bone and the now present bone hole. The length of the opening between the bottom of the screw-hole in the plate and the exit hole of the bone is measured to provide a screw of the appropriate length to account for the thickness of the plate (and its screw hole), as well as the bone itself. The components of depth gauges are configured so as to nest within the holes of the metal plate and account appropriately for the thickness of the plate.
Usually, only one side of the involved bone is readily accessible or visible to the surgeon, so that the depth of the pilot hole must be determined by devices which access the pilot hole from one side. The diameter of the pilot hole is usually slightly smaller than the diameter of the screw to be used so that the threads of the screw can bite or obtain purchase in the bone adjacent to the hole and secure the screw. The mechanics of the appropriate sizes of screws for holding various types and sizes of bones and for use with various fixation devices has been determined in various studies by surgical scientists and vendors of such products and is fairly standardized. In orthopaedic surgery, most screws used vary between about 1 and 5 millimeters in diameter, for example. Lengths may vary from about 8 millimeters up to 10 centimeters and longer depending on the application. Lengths of 10 to 50 millimeters are very commonly used. In most situations, the length of the screw must be measured to within 1-2 millimeters of accuracy. These dimensions, the accessibility of the involved structures in the surgical field, and the situation of a sterile surgical setting do provide some constraint on the size, shape, and type of devices or depth gauges which might be used to measure the pilot holes described.
The ideal depth gauge should be accurate, simple to maneuver, and it should be easy to read the indicated depth. It must be easy to clean thoroughly and capable of being readily sterilized. The device should be easy and relatively inexpensive to manufacture, durable, and mechanically reliable. Ideally, the manipulation of the gauge in all its aspects should be possible with one hand. Oftentimes the surgeon using the gauge may require the other hand to help secure the limb or body part being addressed, to directly hold together the bones of the fracture being fixed, or to support clamps which are holding the fracture. The presence of blood and tissue fragments may interfere with motion of parts which might be more easily mobile in a less harsh environment. While a device which is reuseable after suitable cleaning is consistent with many of the instruments currently used in surgical procedures, designs of a depth gauge, which are suitable for one-time use, are also quite easily conceived. The constraints of anatomy and surgical exposure may limit the ability to position or manipulate the gauge.
A variety of devices, or depth gauges, exist or have been proposed for measuring the length or depth of holes in bone. The prior art devices in current practice are generally based on mechanical principles. These devices exhibit many of the “ideal” characteristics listed hereinbefore and have been used actively in surgical practice for several decades. In general, such mechanical devices have the advantage of relative simplicity for manufacturing and use, durability, and familiarity for operation by those accustomed to working with tools. While some specialized designs exist to function with some specific designs of fixation devices, such as a gauge, which might attach directly to a fixation device and allow measurement of screw length as well as function as a guide for screw placement, most depth gauges are more universal in that they can be used to measure any bone hole. Various sizes of gauges are available, as appropriate, for holes of certain diameter and depth ranges, so that, for instance, gauges for measuring screws used in surgery on bones of the hand are generally scaled differently from those used to measure those of the femur, although the general principles and mechanics of the design may be similar.
Referring to FIGS. 1 and 2, which show examples of prior art gauges, most of the prior art designs in current use can be described as having a nested design in which an outer barrel or sleeve 1 slides over, or relative to, an inner arm or barrel 3 which has a narrow probe 5 at one end. The probe portion usually has a small “J” or hook-like portion 7 at its tip. The width of the hook-like portion 7 of the “J” is limited because the widest dimension of the probe (width of the shaft of the probe 5 plus the width of the protruding “hook” 7) must fit through the pilot hole in the bone, which, in many applications, is only between 1 and 3.5 millimeters wide. The actual extended or hook portion 7 can only be a part of this total width so that the entire width of the tip fits through the pilot hole, but there is enough protrusion of the “hook” to serve as a place to “catch” on the edge of the bone hole. The probe 5 is inserted through the pilot hole and the hook 7 is used to “catch” or grapple on to, the outside edge of the bone at the exit point of the pilot hole. There are other devices which have been proposed, such as, for example, those of Bhattachayyra (U.S. Published Patent Application No. 2006/0224161 A1), which have posited more complex arrangements for “hooking” the far end of the pilot hole. The prior art probe is maintained in position, “hooked” to the opposite side of the bone. The outer barrel or sleeve 1 of the gauge is then advanced against the bone of the outer edge of the entrance site of the hole. The two sides of the bone hole are thus defined and with proper calibration of the relative positions of the probe portion 5 and the outer sleeve 1 portions of the gauge, a scale 9 established and marked on the gauge in its manufacture can be read to indicate the length/depth of the bone hole. The distal portion of the outer barrel 1 which contacts the bone of the near cortex, or entry hole site, usually has a tapered tip with a contour similar to a screw head, so that when a plate is used, the tip portion of the outer barrel can seat down in the screw hole in the plate, and the tip 11 of the outer barrel 1 contacts the depth of the screw hole where the screw head will actually contact the plate and thus accommodates for the thickness of the plate.
Most prior art designs, while useable, suffer significantly in terms of their maneuverability. The existing gauges are such that the proximal portion of the inner barrel portion of the gauge is either flat or a half-cylinder like shape. Usually there are notches or depressions near the end opposite to the probe, which are to accommodate finger holding of this end of the probe. They allow interdigitation of the thumb or fingers on a front notch and a posterior notch to facilitate grasp and manipulation of this element of the gauge. A scale is usually imprinted on one side of the surface proximal to the narrow bone probe for use in reading measurements. The outer barrel often has grooves or a roughened surface to aid in gripping and manipulation of that segment of the gauge.
In a simple description of use, the gauge is grasped with one hand and the probe portion is inserted into the bone hole, and “hooked” against the edge of the exit side of the hole, the outer barrel is advanced down against the near side of the bone, and a reading of screw length is made. While this overall concept is simple and straightforward, the actual manipulation is often difficult. Use is really a five-step process:                1) Inserting the probe through the bone hole;        2) “Hooking” the end of the probe on the exit side of the hole;        3) Maintaining the gauge and probe in a steady “hooked” position;        4) Advancing the outer barrel against the entry side of the hole while maintaining the “hooked” position; and        5) Reading the measurement.        
A detailed examination of these steps helps to understand the problems with current designs.
To use the prior art gauge, the gauge is grasped over the outer barrel and the proximal portion of the inner barrel/probe portion, using the thumb and several or all of the fingers in a manner similar to that used for grasping an object, such as a toothbrush or a table knife, for example. Alternatively, the gauge can be grasped in a similar manner, but only holding onto the proximal portion of the inner barrel. Holding the gauge in this manner, the probe is inserted into and through the pilot hole. When it is judged or felt that the end of the probe has traversed the hole, force is directed to lever the probe portion against the inner walls of the bone hole, and the probe is slowly withdrawn until the “J” hook is felt to catch on the far side of the hole. Maintaining pressure of the probe against the sidewalls of the hole while maintaining a gentle pull or tension in the direction of withdrawing the “hook” is necessary to keep the “J” from disengaging from the edge of the hole and withdrawing back through the pilot hole prior to making a measurement. This allows for positioning of the probe within the bone hole and securing the hook of the probe against the exit surface of the hole. Next, if the entire gauge was grasped, the hand grasping the gauge must be adjusted so that only the proximal portion of the inner sleeve/probe is being held, and the outer barrel is free to slide. Usually the middle, ring, and small fingers, or some combination thereof are curled around this proximal end to secure it and maintain the gauge and probe in a fixed position. Pressure of the probe against the sidewalls of the pilot hole and proximally directed tension on the “hook” must be maintained throughout this process to keep the probe “hooked.” For one-handed use, while holding the probe portion in steady position, the thumb, or thumb and index finger of the grasping hand, is/are then slid or straightened in such a way as to move them toward the bone hole and use them to push against the proximal end of the outer barrel and advance or slide it over the inner probe until the outer barrel contacts the bone at the entry site of the hole. In this position, a marking on the outer barrel is aligned with the scale marked on the inner barrel, and a reading of length of the desired pin or screw can be made. For the less-preferred, two-handed use, while the first hand maintains position of the probe, the opposite hand is used to grasp the outer barrel and advance it into position. There are some minor variations in the exact shape and way of marking scales for the various gauges in current use, but they are all similar.
In practice, there are several difficulties with manipulation as described and as the gauge is designed to be operated.
Inserting the probe portion can sometimes be difficult if bone fragments or other tissues block part or all of the hole. Usually, this portion of use can be accomplished because, if needed, the whole gauge can be grasped firmly enough to wield it in a forceful manner.
During the phase in which the probe is being “hooked,” the balance of forces to hold pressure on the sidewalls of the hole and slight withdrawal tension on the “hook” can be somewhat difficult to maintain with the type of grasp which must be used. The forces must be exerted in part or in whole by the wrist and arm rather than just movements of the fingers because the fingers are held in a nearly fully flexed position to maintain the grasp on the gauge itself. These forces of the wrist and arm are grosser with less fine control of force and position than those which are controlled just by finger motion.
Once the probe is positioned and “hooked” as described hereinbefore, maintaining the position of the hook with the grasping technique noted is of limited security because of the nature of holding a narrow, elongated structure in such manner. A good example of this instability can be demonstrated by holding the end of a pen opposite from the point by curling some combination of the middle, ring, and small fingers around it for support or even by pinching it between the thumb and one or several fingers. If one tries to push the point end of the pen to deflect it in another direction, it is fairly easy to deflect unless one is grasping along the majority of the barrel of the pen with more of the hand/fingers. Such grasp of the depth gauge is not possible except during insertion of the probe, as the outer barrel portion ultimately needs to be free to slide over the inner, probe portion. Again, the forces maintaining the gauge and probe in position must be largely exerted by the wrist and arm.
Other factors also contribute to difficulty in maintaining the position of the “probe/hook.” The grasp of the “hook” is somewhat tentative due to the relatively small size of the “hook.” The edge of the bone hole which is being hooked may be slightly rounded as well due to the nature of bone substance. These aspects contribute to making it relatively easy to cause the hook to disengage, and in fact, it is not unusual to have to reset the “hook” several times during the measuring process. These factors necessitate a way to provide fine control of the gauge to resist loss of position during measurements.
For one-handed use, it is biomechanically difficult to maintain a grasp on the proximal end portion of the probe, keeping lateral pressure of the end of the probe against the walls of the hole and proximal directed force (away from the hole) on the probe to keep the “hook” “set,” and then, with the same hand, direct movement of the thumb or thumb/index finger toward the hole to advance the outer barrel. The competing forces of pushing toward the hole with part of the hand and pulling away from the hole with another part of the hand is difficult with the configuration of the usual gauges. This is in part again due to the fact that the probe position must be maintained in part by the relatively gross forces and control associated with wrist and arm muscles relative to those of the hand.
During the phase of advancing the outer barrel, because of the forces directed toward the hole, sometimes, the entire gauge including the probe portion is advanced so the “hook” is no longer against the edge of the exit hole. This necessitates resetting the “hook,” or if not recognized, results in overestimating the length of the required screw. The force needed to hold the probe against the side walls of the hole to keep the probe “hooked” also can cause bending of the probe and to a small degree the rest of the inner barrel. This deformation can make it mechanically more difficult for the outer barrel to slide because of increased friction. Presence of blood and/or tissue fragments which may adhere to the gauge may also interfere with easy sliding of the outer barrel. The nature of the contrasting motions needed to maintain the position of the probe and advance the outer barrel when combined with these other factors can make it difficult to use current gauges.
Often, the surgeon must hold the inner barrel and probe in position with one hand and slide the outer barrel with the other hand to successfully make a measurement. This can be problematic if the other hand is needed to hold the fracture or is otherwise employed in the surgical procedure, such as holding other instruments. Even with two-handed use, it can sometimes be difficult to balance the forces as the motions of the probe and the outer barrel are still done by wrist and arm movements, while the fingers are just used to maintain grasp on the parts of the device.
The contours, configurations, and biomechanics of operation of depth gauges currently in use, while resulting in useable devices, leave room for significant improvements in design, particularly as it relates to the ability to grasp the device, the ability to manipulate the device in a more biomechanically optimal way for the human hand, and the ability to manipulate the device with one hand during the various stages of operation necessary to measure the length of a hole in bone.
Vogelman, U.S. Pat. No. 3,958,570, while not disclosing a depth gauge, discloses elements of a syringe including those of what in current medical and surgical practice is often referred to as a “control syringe.” The syringe also consists of two main elements with an inner sleeve or plunger and an outer barrel, which acts as a container for substances which are withdrawn into the syringe or ejected out of the syringe. These elements are also slidably connected. Vogelman discloses the placement of rings on the sleeves with one ring on the plunger and two rings on the outer sleeve or barrel. These allow firmer grip on the syringe and allow the plunger to be pushed with “considerable force.” In fact, syringes with such ring attachments are in common use in the medical field and constitute the so-called “control syringe.”
Guyer, U.S. Pat. No. 5,928,243 discloses a device with features typical of depth gauges which are currently used in the field of orthopaedic and other surgeries. The device includes a body, or outer barrel, and an inner sleeve, or shaft, which includes a probe portion. The two pieces are slidably connected and the inner shaft has markings which allow for measurement of the depth of bone holes. Typically, various sizes of such gauges are available with appropriate dimensions to make measurements for the sizes of screws typically used in surgical practice. The depth gauge of Guyer discusses a device very representative of those in current use and can be thought of as a “reversed” or “inverted” syringe. With a syringe, the outer barrel provides, in essence, a cannula for sliding of the plunger portion of the syringe. The barrel also contains any fluids or substances which are injected or withdrawn into the syringe. In its common usage the outer barrel also essentially contains a “probe” which in practice, is a needle. To use the syringe, the probe and outer barrel are set into position by manually advancing the needle into the site for injection (or site of withdrawal in the case of blood sampling) by gripping the barrel to which it is attached and using the barrel as a handle to manipulate the needle. The barrel and needle are then supported in position, and the plunger is advanced in the case of injection and withdrawn in the case of sampling. Advancing the plunger is usually done by pushing on the cap of the plunger with the thumb; although, a finger could be used. On simple syringes, flanges on the sides of the outer barrel allow counter-pressure against the advancing plunger by placing two fingers against the flanges. In a “control syringe,” the flanges on the outer barrel and the cap of the plunger are replaced by rings which allow greater control and support and easier movement of the involved parts. The rings allow easier, one-handed use in most cases. In a depth gauge, the action is reversed. The inner sleeve and probe of the depth gauge corresponds to the outer barrel and needle of the syringe, and the outer barrel of the depth gauge most closely approximates the action of the plunger or inner barrel of the syringe. The inner sleeve and probe are positioned and set in place, and the outer barrel is then slid over the inner sleeve to achieve the final set position, which allows a measurement to be read from the gauge. In the syringe, the outer barrel and probe/needle are set, and the inner barrel (plunger) is advanced.
Novel features of the current invention include incorporation of ring handles in a particular and novel configuration for manipulating portions of a depth gauge. These are incorporated in a specific arrangement of design which enables the user to easily manipulate the device with one hand in all phases of its use and to do so in a manner which best utilizes the inherent biomechanics of the human hand as it relates to its ability to provide fine motor control and sensory feedback, which contributes to that control.
Middleman, U.S. Pat. No. 5,486,183, and Beecher, U.S. Pat. No. 4,243,040 disclose devices for use in surgery in which a probe or instrument is passed through an outer cannula or sleeve and in which the outer sleeve is controlled by one or more attached ring handles to accommodate finger grip, and the central portion or probe is controlled with a single ring handle intended for manipulation by the thumb. Beecher also teaches a swiveling type of arrangement for a single ring handle to better accommodate position of the digit being used to operate that ring.
Pettine, U.S. Pat. No. 5,242,448, discloses a bone probe which demonstrates as part of it, a ring-type handle on the probe portion. Again, this would allow manipulation of that probe portion which is set up mechanically to move in a way similar to the central plunger on a syringe, i.e., by use of the thumb in the ring of the central element, to advance and retract that element.
Cunningham, U.S. Pat. No. 4,033,043, teaches a device for measuring the length of an opening which can be operated in a one-handed fashion by means of gripping handles and levers. The design is more complex and mechanically different than that of the current invention.
Bhattacharyya, U.S. Published Patent Application No. 2006/0224161 A1, discloses a depth gauge apparatus which essentially has three parts. There is an outer barrel or sleeve and an inner barrel, which includes a probe portion. These two pieces are nested and slide relative to one another. The third portion is a mobile “spreader” device which is used to expand the tip of the probe to facilitate its ability to “hook” onto the edges of a bone hole. This patent also shows the use of rings to control the various elements with one ring for each of the three main elements shown in the exemplary embodiment. The function of this device requires proximal withdrawal of the central spreader to expand the tip of the probe, holding the inner barrel down with the one ring shown attached to it, and then, while maintaining this position, the outer barrel must be advanced distally (toward the bone hole) utilizing the ring attached to it. With the configuration of this device, knowledge of the biomechanics of the hand would dictate that to operate this device, one would need to place the thumb in the ring for the spreader, and two fingers, most likely the index and middle fingers, each in one of the other two rings. Depending on the orientation of the scale for reading measurements, most likely, the index finger would be placed in the ring for the outer barrel and the middle finger in the ring for the inner sleeve. To operate this then requires the thumb to extend to withdraw the spreader. The middle finger then holds the inner barrel steady, and the index finger must then be extended to advance the outer barrel. This combination of movements, extending the thumb, holding the middle finger and its barrel steady, and extending the index finger and advancing its barrel, would likely prove quite awkward in practice. While it is feasible, it is not the optimal utilization of the mechanics of the hand.
There remains, therefore, a very real and substantial need for an improved bone depth gauge and associated method which may be easily employed by medical personnel using one hand to accurately measure the depth of a bone passageway.